The present invention relates to wood lathes and particularly to a vacuum chuck for holding a workpiece on a face plate of a wood lathe.
It is desirable to attach a workpiece to a faceplate or similar rotating portion of a lathe in such a way that no marks or impressions are made on the workpiece as a result of the fastening, so that workpieces such as wooden bowls or plates can be provided with a uniformly polished and attractive surface, both on top and on the bottom.
Staunton U.S. Pat. No. 1,130,679 discloses a vacuum chuck for a lathe, in which a disc of soft rubber is used to act as a seal on the workpiece held against the disc by use of a vacuum.
Richardson U.S. Pat. No. 2,444,531 discloses a cup-like faceplate connected to a vacuum source through a swivel connection. The apparatus disclosed, however, would require significant modification of a lathe for its use.
Granata U.S. Pat. No. 2,852,264 discloses a vacuum chuck in which a vacuum pump is connected to a faceplate through a swivel connection mated with the spindle bore of the lathe by a simple tapered plug. Such connection of the vacuum tube to the lathe spindle appears to offer little if any security against being dislodged merely by the rotation of the lathe spindle if there is any imbalance or misalignment.
Foley et al. U.S. Pat. No. 5,062,384 discloses a rotary seal for a vacuum chuck. Such a seal, however, does not appear to be readily useful with an ordinary wood lathe.
Other vacuum chuck devices for use with conventional wood lathes are available, but they are apparently not capable of handling more than a small vacuum nor of safe operation at higher speeds.
When turning wooden bowls or plates, for example, it is desirable to rotate the workpiece at a speed high enough to cut away portions of the workpiece in a reasonably short time using a light cut or relatively fine abrasives. Traditionally, speeds of 300-400 rpm were used, but speeds approaching 1000 rpm are now desired by some. Use of higher speeds, however, requires a rotary vacuum coupling to be attached to a lathe spindle in such a manner that rotation in the rotary coupling will take place concentric with rotation of the lathe spindle, in order to avoid destructive vibration. Use of higher rotational speeds or attachment of larger workpieces to a lathe faceplate requires vacuum on the order of several inches of mercury, since a workpiece must be securely attached to a faceplate. Separation of a workpiece from a faceplate rotating at high speed is likely to be disastrous, since a workpiece would be likely to leave the faceplate at a tremendous velocity and with sufficient momentum to injure a person seriously, not to mention destruction of the workpiece.
Not only is it desirable to be able to support a workpiece on a face plate in the normal location above the ways of a lathe, but for larger workpieces than can be accommodated within the usual radial capacity of a lathe it is desirable to use a vacuum chuck incorporating a faceplate located on the outboard end of a lathe spindle.
What is needed, then, is a vacuum chuck which can be installed easily and securely on a lathe to enable a lathe to be operated at a variety of rotational speeds and to hold large workpieces securely.